Conventional foundry binders include both a phenol formaldehyde component and an organic polyisocyanate component. Foundry mixes are prepared by mixing the binder with a foundry aggregate. Foundry shapes (molds and cores) are typically prepared by shaping the mix and curing the foundry shape with a liquid or gaseous tertiary amine curing catalyst.
One of the major processes used in the foundry industry for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry mix which is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
One of the processes used in sand casting for making molds and cores is the “cold-box” process. In this process a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. An alternative process is the “no bake” method, that involves the use of liquid catalysts such as tertiary liquid amines.
A phenolic-urethane binder system commonly used in the cold-box process is cured with a gaseous tertiary amine catalyst. See for example U.S. Pat. Nos. 3,409,579, 3,429,848, 3,432,457, and 3,676,392. The phenolic-urethane binder system usually consists of a phenolic resin component and poly-isocyanate component which are mixed with sand prior to compacting and curing to form a foundry mix. Such phenolic-urethane binders used in the cold-box process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1400 C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 800 C.
There are disadvantages to using phenolic resin systems, regardless of whether the system is filled (e.g., with aggregate) or unfilled, e.g., for use in other applications.
With regard to filled systems, there are disadvantages to using phenolic-urethane binders in the cold-box process. Both the phenolic resin component and polyisocyanate component generally contain a substantial amount of organic solvent which can be obnoxious to smell. Additionally, these binders contain small amounts of free (i.e., unreacted) formaldehyde and free (i.e., unreacted) phenol which may be undesirable. Because of this, there is an interest in developing polymer systems, including for use as binders, which do not use organic solvents and do not contain free formaldehyde or free phenol. Additionally, when the two components of the phenolic-urethane binder system are mixed with the sand to form a foundry mix, they may prematurely react prior to curing with the gaseous catalyst. If this reaction occurs, it will reduce the flowability of the foundry mix when it is used for making molds and cores, and the resulting molds and cores will have reduced strengths.